The present invention relates to a troughing idler for use in supporting a conveyor belt in a troughed conveyor system. More specifically, the present invention relates to a troughing idler that includes a pair of center rolls that each have a larger outer diameter than a pair of side troughing rolls in order to reduce the indentation resistance of the troughing idler. Further, the present invention relates to a troughing idler in which the center rolls are mounted between a pair of pivot brackets whose rotation is limited by a pivot limiting mechanism.
Troughed belt conveyor systems have long been used to transport bulk material from one location to another. Troughed belt conveyors are particularly useful in transferring bulk material between distant points at a mine or quarry. Typically, the troughed belt conveyor system includes a series of spaced troughing idler assemblies positioned along the length of a moving conveyor belt to support the conveyor belt over its length. Each of the troughing idlers includes a rotatable center idler roll and a pair of side troughing idler rolls that are positioned at a troughing angle relative to the center roll to define the trough for transporting the bulk material.
The amount of force required to move the belt and bulk material over a troughing idler including the center roll and pair of side troughing rolls depends on two main components which include the turning resistance required to rotate each of the troughing rolls and the center roll and the rolling resistance of the belt and the material as they travel over the idler rolls of the troughing idler.
Generally, the turning resistance required to rotate each of the rolls of the troughing idler can be broken down into two main components which include the resistance of the roll to turning about the shaft due to bearing, seal, grease and other frictional resistances and the resistance due to sliding of the belt over the rolls of a misaligned idler. The rolling resistance can be broken down into three main components which include the resistance due to the indentation of the rolls into the conveyor belt, the resistance due to the flexure of the belt over the idler rolls, and the resistance due to the flexure of the material over the idler rolls.
As can be understood by the above discussion, a reduction in the resistance in any one of the areas listed increases the efficiency of the troughed belt conveyor system and thus requires less energy to transport the same amount of material.
The indentation resistance discussed above is caused by the idler rolls indenting in the bottom cover of the conveyor belt under the weight of the belt and the supported material. Referring now to FIG. 7, the weight of the material on the belt sets up a contact pressure distribution as illustrated by the area 10 shown in FIG. 7. The contact pressure can be resolved into a vertical force 12 by integrating the pressure over the contact length. The pressure distribution is symmetrical about the centerline of the idler roll 14 when the conveyor belt 16 is stopped. Therefore, the vertical contact force 12, which acts through the centroid of the pressure distribution, is on the centerline of the idler roll 14.
However, when the conveyor belt 16 is moving, the viscoelastic properties of the rubber cause a non-symmetrical pressure distribution as illustrated in FIG. 8. When the conveyor belt 16 is moving, the conveyor belt 16 is indented (compressed) on the approach side of the centerline of the idler roller 14. On the opposite side of the centerline, the rubber, due to its natural properties, is unable to uncompress fast enough and the contact length on the downstream side of the centerline of the idler roll is shortened. As illustrated in FIG. 8, the conveyor belt 16 loses contact with the idler roll at position 18 and does not fully relax until position 20. Because of the shortened contact link, the contact pressure increases, as illustrated by area 22. Additionally, the vertical contact force, as illustrated by arrow 24, is now non-symmetrical with the centerline of the idler roll 14 such that the vertical force 24 is offset toward the upstream, approach side from the centerline of the idler roll 14. The offset of the vertical force 24 causes a moment that must be compensated for by a horizontal force 26 tangent to the idler roll 14. The horizontal force 26 times the radius of the idler roll 14 must equal the vertical contact force 24 times the distance it is offset from the centerline. This horizontal force 26 represents the indentation rolling resistance.
As can be understood by the discussion above, decreasing the amount of indentation resistance caused by the idler rolls indenting will result in more efficient operation of the troughed belt conveyor system and thus in energy savings by the owner of the conveyor system. Additionally, a reduction in the resistance due to the flexure of the belt over the idler rolls and the resistance due to the flexure of the material over the idler rolls further increases the efficiency of the conveyor system. Therefore, it is an object of the present invention to provide a troughing idler for use in a troughed belt conveyor system that reduces the amount of indentation resistance and the amount of belt and material resistance.
The present invention is a troughing idler for use in supporting a moving conveyor belt of a troughed belt conveyor. The troughing idler generally includes a support frame extending along that mounts a pair of side troughing rolls at a troughing angle. In addition to the pair of side troughing rolls, the troughing idler of the present invention includes a pair of center rolls spaced from each other. The rotational axes of each center roll are parallel to each other and are spaced a common distance from the longitudinal axis of the support frame. The center rolls are each rotatably mounted between a pair of pivot brackets that are pivotable about a center pivot shaft. The pivot shaft extends along the longitudinal axis of the support frame such that the center rolls are equally spaced from the longitudinal axis of the support frame.
The pivotal rotation of the pair of pivot brackets is restricted and controlled by a pivot limiting mechanism of the present invention. The pivot limiting mechanism allows the pair of pivot brackets to rotate about a center pivot shaft in order to equalize the load felt by each of the center rolls. The equalization of the load across the pair of center rolls aids in reducing the energy consumed by the rotation of the center rolls. In the present invention, the pivot limiting mechanism includes a stop member mounted to the pivot brackets to limit the maximum rotation of the pivot brackets. The limitation on the pivoting motion of the pivot brackets prevents the pivot brackets from over-rotating into contact with the moving conveyor belt should one of the center rolls become dislodged from the pivot bracket.
In accordance with the present invention, the outer diameter of the two center rolls are equal such that the center rolls equally split the forces from the moving conveyor belt between the two center rolls. In prior art troughing idlers, the center roll and the pair of side troughing rolls have the same outer diameter such that a single size idler roll can be used as either of the side troughing rolls or either of the center rolls. In the present invention, the outer diameter of each of the center rolls is greater than the outer diameter of the two side troughing rolls. Preferably, the outer diameter of each of the center rolls is at least one inch larger than the outer diameter of the side troughing rolls. The increase in the outer diameter of the center rolls, along with utilizing two center rolls rather than a single center roll, greatly reduces the total indentation resistance for the troughing idler.
The troughing idler of the present invention therefore includes a pair of center rolls spaced from each other in a direction parallel to the direction of travel of the conveyor belt being supported by the troughing idler. The fore/aft configuration of the pair of center rolls functions to reduce both the belt and material flexure resistance for the troughing idler. Additionally, the pair of center rolls in the troughing idler of the present invention each have an outer diameter greater than the outer diameter of the pair of side troughing rolls. The combination of the increased diameter of the center rolls as well as the split of the center roll into two center rolls greatly reduces the amount of total indentation resistance for the troughing idler.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.